The invention relates to a DEPFET transistor.
In semiconductor detectors for high sensitivity radiation detection, DEPFET transistors (DEPFET: Depleted Field Effect Transistor) are used as the readout element, these having been invented in 1984 by J. Kemmer and G. Lutz and being described for example in Gerhard Lutz: “Semiconductor Radiation Detectors”, 2nd edition, Springer-Verlag 2001, 234-253.
The radiation to be detected here generates signal charge carriers in the semiconductor detector, which signal charge carriers are detected by the DEPFET transistor serving as a readout element. The DEPFET transistor then generates an output signal (e.g. source voltage) as a function of the radiation-generated signal charge carriers in accordance with a specific characteristic curve, which output signal forms a measure for the radiation to be detected.
In such semiconductor detectors a non-linear characteristic curve is desirable, with a steep characteristic curve slope in the case of small signal charges and a gentle characteristic curve slope in the case of large signal charges.
The steep characteristic curve slope in the case of small signal charges is advantageous, since then small signal charges and correspondingly weak levels of radiation may be measured with high measurement sensitivity.
The gentle characteristic curve slope in the case of large signal charges is advantageous, on the other hand, because otherwise the measurement range would be exceeded by large signal charges.
Such a non-linear characteristic curve thus advantageously combines high measurement sensitivity in the case of small signal charges with a large measurement range.
This non-linear characteristic curve is achieved in the case of conventional semiconductor detectors by a suitable electrical connection arrangement for the semiconductor detector, such as for example by non-linearity in the feedback branch or an amplifier range changeover as a function of the detected signal. Such a semiconductor detector is known from DE 10 2005 025 641 A1.
A disadvantage of known semiconductor detectors with a DEPFET transistor as readout element is therefore the fact that the desired non-linear characteristic curve has to be achieved by a separate electrical connection arrangement, which is associated with additional circuit complexity.
A semiconductor detector is also known from WO 2007/077287 A1, which does not however comprise a DEPFET transistor.
Finally, reference is also made to US 2005/0167771 A1 as general prior art.
The object of the invention is therefore to reduce the effort required to bring about the desired non-linear characteristic curve for a semiconductor detector.
This object is achieved by a DEPFET transistor according to the invention.